The first woman to become a British prime minister; the first prime minister in more than 150 years to enjoy three consecutive terms (and the 1990s are beckoning); the first British politician whose very name embodies an ideology - ``Thatcherism''; the British champion of a rightist trend in the advanced industrial democracies, including the United States; and the most combative, self-righteous, and also victorious British leader in memory.

All the more reason to take Thatcherism seriously, and not dismiss it either as an aberrant passion by an electorate momentarily seduced by state-sponsored consumerism, or as the deserved triumph of common-sense patriots over the loony left and the wimpy center.

While providing the basic facts and chronology, Kenneth Harris's hagiography of Thatcher offers little more, not insight, analysis, grace, or explanation. By contrast, Peter Jenkins's ``Mrs. Thatcher's Revolution'' is a work of brilliance - perhaps even of genius - rich in context, in telling detail, and in the dynamism and conflict that make politics the most demanding game of all. For Thatcher has vanquished the Argentines (and a thousand men died), the trade unions, the ultra-left inner-city councils, the civil service mandarins, the conciliatory ``wets'' of her own party, the free-speech advocates of ``Spycatcher,'' and both Labour and its would-be successor, the Social Democrats.

In so doing, she has battled an idea: full employment and labor peace at any price, be that price inflation, inefficiency, low productivity, or overweening union power. This doctrine, though linked to Keynesian economics - Thatcher's pet hatred - really stems from the 1930s depression, from traumatic memories of defeated men lining up for the dole.

Thatcher rejects such memories, as Peter Jenkins demonstrated in telling asides about her experience and outlook. He is brilliant on the inner springs of Thatcherism, its monetarism `a la Friedrich von Hayek and Milton Friedman, its purgatives of austerity and deflation, its avowal of individualism over Whitehall's commands. He sees it as a struggle movement, the triumph of ``conviction politics'' over the 40-year consensus of the Labour/Conservative mainstream.

The struggle continues. She is now battling the universities, the outlawed Irish Republican Army (which almost assassinated her in 1984), and the European Community, against whose social democratic and centralizing inclinations she invokes free enterprise, the market economy, and British uniqueness. Her ultimate goal is eradicating socialism in Britain, striking at its inner-city strongholds in London and the North.

In so doing, she has privatized government-owned housing and businesses, fostering entrepreneurship and a new conservative constituency of working-class homeowners: There are Thatcher Labourites just as there are Reagan Democrats. Like Reaganism - and social Darwinism - Thatcherism bets on the strong and rejects the underclass.

Jenkins argues convincingly that this began with Britain's economic decline in the 1950s, gathered strength as the situation worsened in the 1970s, and culminated in 1978-79, the strike-torn ``Winter of Discontent,'' when the old Labour/Conservative consensus disintegrated.

Enter Mrs. Thatcher, a right-wing ``savior,'' with economic revival as her promise. North Sea oil has helped her, as has international prosperity. But have there been structural changes that offer sustained growth?

Here Jenkins is cautious. For Thatcher is essentially a moralist, stronger in rhetoric about hard work and risk-taking than in developing industrial policy, which, after all, entails the government direction she rejects: Japan is a rival, not a model. The Thatcher revolution will consolidate itself only by delivering the goods, and the jury is still out.

But one verdict is clear: Socialism is played out, exhausted. Hence Jenkins's subtitle - ``The Ending of the Socialist Era'' - which forms the book's essential thrust. The attempt of socialism and its variants - social democracy, the welfare state, even the New Deal - to mitigate the inequalities of capitalism has been the dominant world ideal of this century.

Jenkins, an honest centrist with no ax to grind, is obviously pulled by the great socialist tradition of humanism and compassion.

Socialism, however, focuses on redistribution, not on production, and so has become irrelevant to the faltering industrial states, and even more so to the Soviet empire. Thatcherism embodies these issues. ``She, more powerfully than anyone else,'' writes Jenkins, ``has articulated the moral doubts and yearnings of her age.... The future may not be hers but she has set its agenda.''